Redox resins



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United States Patent N0 Drawing. Application July 26, 1954 Serial N0.444,649 V 3 Claims. (Cl. 260-5I) This invention relates to certainpclyhydroxyphenolaldehyde resins which function as reversible electronexchangers, and is a Continuation in part of my application forredoxresins iiled June 8, 1953, serial number 360,367, now abandoned. Theseresins are cross linked, and hence, are infusible and insoluble in allsolvents. In their reduced form these polymers act as electron donorsand in their oxidized form as electron acceptors. Since hydrogen ionaccompanies each electron transfer, these resins may be calledhydrogendonors or hydrogen accep- Unlike the common oxidants and reductantswhich remain in solution together with their reaction products, theseredox resins, being totally insoluble in both the reduced and oxidizedstates, add no foreign matter to any prospective reactant. In thisrespect these materials behave like hydrogen adsorbed on a metalcatalyst. The

hydrogenation is carried out without any contamination because of thetotal insolubility of the catalyst.

Some redox resins have been prepared by Cassidy and his co-workers. Hisearly work on thermal polymerization of vinyl hydroquinone yieldedrather low molecular weight products as shown by their solubility inmany common solvents such as ether, alcohol, and, acetone. Suchmaterials would have little value in columns or beds for electronexchange. However, his most recent work on the copolymerization of vinylhydroquinone and divinyl benzene yields 'a resin insoluble in the commonsolvents. This latest composition is purported to be a useful redoxmaterial.

i Cassidy proposed hydroquinone-formaldehyde polymers as possible redoxresins. Such resins were prepared by me in both aqueous and glacialacetic acid'solution in the presence of sulfuric acid as a catalyst.Contrary to the behavior of catechol-aldehyde, pyrogallol-aldehyde, andother polyphenolaldehyde resins in which the phenolic groups areadjacent on an aromatic ring, the hydroquinoneeformaldehyde resins werefound to have little reducing action on ferric ion, ferricyanide ion,and iodine. These reductants were chosen as examples of the three.general types, namely, cationic, anionic, and neutral respectively. 7

Among others, there are two possible reasons for this difference inbehavior-between aldehyde resins of ortho and para dihydroxy phenols.The first is a steric conrsiderat-ion. The hydroxyl groups in thehydroquinone polymers are surrounded either by a substituent initiallypresent or by a group derivedfrom the aldehyde linking rings with oneanother. Such a situation severely hinders the approach of a reduciblemolecule or'ion. This efiect becomes greater as the linking groupincreases in bulk, "eig. in going from formaldehyde to fur'fural. In thecase of catechol, however, the proximity of the hydroxyl groups permitsa larger free surface area for a reactant to approach the reaction site.

"The secondreason is the synergistic action of the adjafcent 'hydroxylgroups in the formation of chelates with metallic ions. Electrontransfer follows chelation in the cases ofth'ose oxidizing cationshaving high enough potenadjusted so that gelation occurs in ten hours.

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2 tials. This chelating property is impossible in the case of the paradihydroxy phenols.

The mode of preparation of these resins is of prime importance. Severalinvestigators including myself have reacted catechol, pyrogallol, andsimilar phenols with formaldehyde and furfural in water solution usingstrong inorganic acid catalysts. The recipe given consists ofcodissolving all the materials in water, boiling the solution until thepolymer has precipitated, filtering, washing free of solubles, anddrying. The resulting polymers are finely divided brown or blackpowders. These materials have good redox capacity but suffer fromdimensional instability. During any redox cycle some of the resin breaksdown to give microscopic as well as colloidal particles. The breakdownproducts filter through one inch thick glass wool or paper plugs.Whether this behavior is due to insufficient cross linking of the resinprepared in the above manner in aqueous solution, or to chemicalbreakdown by the reagents used during the cycle has not been resolved.However, I have found that if an organic solvent in lieu of water isused in the above recipe, the amount of observable breakdown during useis nil. I have also found that water may be used as a reaction medium toproduce a dimensionally stable resin if and only if the solution of thereactants is set aside at or below room temperature to form a gel. Thisgel can then be hardened by heating with aqueous acid. The priorformation of gels has the added advantage of allowing control of theparticle size distribution of the final product. The gel mass can bebroken down to size requirement.

The following paragraphs summarize the manner of preparation ofdimensionally stable resins of the redox type discussed herein in threedifferent types of media.

1. USE OF WATER AS A SOLVENT In the use of water as a solvent a solutionof the reactants is prepared and set aside at room temperature or belowuntil gelation sets in. The rate of this reaction depends on the natureand concentration of the reactants, the temperature, the catalystconcentration, etc. In my experience this stage may take from tenminutes to a month. In most cases the controlling variables may be Thegel is then broken up into the desired particle size, and the mixture isboiled from one to ten hours. This step causes thorough cross linkingand, hence, produces a resin which is infusible and insoluble in thecommon solvents. Materials prepared in this way show excellent stabilityin use on redox cycles.

2. USE OF ORGANIC SOLVENTS Organic solvents are excellent media forcarrying out these polymerizations. Dimensionally stable resins areprepared by cosolution of the reactants and catalyst fol lowed byrefluxing for periods of /2 to 10 hours. However, if one wishes tocontrol particle size, one should go through the gelation step asdescribed in the previous paragraph. Solvents such as alcohols, ethers,ketones, Cellosolves, carboxylic acids have been found to be excellentfor this purpose.

3. USE OF ORGANIC DISPERSION MEDIA These resins can be prepared asspheroidal particles by dispersing a solution of the required polyphenolin the aldehyde or aldehyde derivative in a hydrocarbon or chlorinatedhydrocarbon medium. Ligroin, kerosene, and hexyl chloride serve well.The dispersion is heated to 60 -120 C. followed by the dropwise additionof 96% sulfuric acid as the catalyst. Stirring and heating is com tinuedfrom one to fifteen hours, i.e. until hardened spheroidal particles areformed. The size distribution depends on such factors as temperature,stirring rate, nature of reactants, etc. An emulsifier may also be usedin the reaction medium to further modify size distribution.

In all of these preparations a molar ratio of aldehyde to polyphenolgreater than 1 must be used in order to get cross linking. If a ratioless than 1 is used, such as in the work of Rhodes, low molecularweight, soluble, fusible polymers result. This ratio is most importantin controlling the degree of cross linking. In practice ratios of 1 to 2/2 have been used. I

I have found that besides aldehydes per se, many derivatives thereofgive substantially the same polymers. Ex-

amples of suchderivatives are acetals, hemiacetals, enol acetates,alkylidene diacetates, and dienolic anhydrides such as furan. Dependingon the nature of the solvent, these derivatives may or may not beconverted to the parent aldehyde. For example, if furan is reacted witha polyphenol in aqueous acid, some of it will undoubtedly be hydrolyzedto succindialdehyde. In glacial acetic acid as the solvent furan wouldprobably be solvolyzed to the dienol diacetate of succindialdehyde, inmethanol to the corresponding hemiacetal or acetal, etc.

The term polyhydroxyphenols as used in this application is limited tothose derivatives which have at least two hydroxyl groups adjacent toone another on an aromatic ring or to those which have at least twohydroxyl groups on aromatic carbon atoms separated by one or twoaromatic carbon atoms incapable of bearing hydrogen or any substituent.All of these derivatives form quinones on oxidation. Further, it isessential that at least one unsubstituted position be present in orderfor condensation with aldehydes to be possible. Examples of suchpolyphenols having one aromatic ring are catechol, pyrogallol, and1,2,4,5 tetrahydroxybenzene. Some derivatives of biphenyl which fallintothis category are: 2,2 dihydroxybiphenyl and 2,2',4,4'tetrahydroxybiphenyl. Similar derivatives of naphthalene are: 1,2dihydroxy naphthalene; 1,4,5 trihydroxynaphthalene (prepared byreduction of the natural quinone, juglone); 1,4,5,8tetrahydroxynaphthalene (preparable from naphthazarine by reduction).2,2 Dihydroxybiphenyl and 1,4,5 trihydroxy naphthalene are examples inwhich chelation of metallic ions occurs even though the electron donorgroups are in separate rings.

I have found that phenols of the above defined class may have othersubstituents present in addition to the requirements stated. Forexample, gallic acid, catechol sulfonic acid, and 1,2 dihydroxy,4-naphthalene sulfonic acid yield excellent polymers. It is verypossible to substitute in the final polymer with other groups. Some ofthe prepared resins are easily sulfonated in the cold with 96% sulfuricacid.

In the case of polyphenols like penta hydroxybenzene or the isomerictetrahydroxy benzenes, which have fewer than three unsubstitutedpositions on the ring, it is necessary to copolymerize such compoundswith catechol or other compounds capable of undergoing cross linking.

The preparations carried out are summarized in Table I. The variousmethods used for these preparations are described below. Table I showswhich variation was applied in each particular case.

Method 1 55 grams of catechol, 100 ml. of 37% aqueous formaldehyde weredissolved in 500 ml. water and the solution cooled down to C. in an icebath. To this solu tion 30 ml. of 37% aqueous hydrochloric acid wasadded keeping the temperature between 0 to 20 C. The mixture was allowedto stand at 20 30 C. until gelation took place. It was broken down intosmall pieces, diluted with l liter of 5% hydrochloric acid, and refluxedfor one hour. After cooling the precipitate was filtered, washed withmany portions of hot water to leach out all solubles, and air dried.

Variations of this experiment showed that the smaller 4 the acidconcentration and the less the heating time, the lighter the color ofthe final product.

It was also found in some cases that the resin could be purged ofsolubles more readily by boiling with organic solvents such as methanol,ethanol, glacial acetic acid or acetone. A final wash with ether aidedin drying the product.

- Method 2 25 grams of pyrogallol, 50 ml. methanol and 40 ml. furfuralwere codissolved and cooled to 15 C. To this solution hydrochloric acidgas was passed in until saturation. After gelation the mixture wasdiluted with 500 ml. methanol containing 5% hydrochloric acid (passed inas a gas), and the mixture boiled for 4 hours. The polymer was broken upand washed with several portions of boiling methanol. It was then dried.

Method 3 25 grams of pyrogallol, 40 ml. fnrfural, 400 ml. glacial aceticacid were codissolved. A mixture of 15 grams of anhydrous aluminumchloride in ml. glacial acetic acid was addeddropwise over a period of15 minutes. The mixture was then boiled for 3 hours, allowed to standovernight, filtered, boiled up with several portions of methanol toextract all solubles, and finally air dried.

Method 4 25 grams of pyrogallol, 40 ml. furfural, 400 ml. glacial aceticacid were codissolved. A solution of 25 ml. 96% sulfuric acid in 100 ml.glacial acetic acid was quickly added. The mixture Was allowed to standuntil gelation set in. The gel was broken up, and boiled up with 400 ml.of glacial acetic acid containing 10 ml. of 96% sulfuric acid. Afterfiltering, boiling up with several portions of ethanol, it was airdried.

Method 5 25 grs. catechol, 15 grams of trioxane, and 250 ml. ofanhydrous formic acid were codissolved. After passing in dryhydrochloric acid gas until saturation, the solution was refluxed withstirring for 3 hours. The product was worked up as given method 3.

Method 6 Method 7 12 grams of 2,5 dihydroxy para quinone were suspendedin ml. glacial acetic acid. 25 grams of zinc dust were added and thesolution refluxed while hydrochloric acid gas was passed inintermittently. The quinone was converted to 1,2,4,5 tetrahydroxybenzene after one hour of this treatment. 5 grams of trioxa'ne were thenadded and the mixture boiled for another 2 hours. The resulting polymerwas worked up by filtration,.boiled up with aqueous HCl to dissolve anyremaining zinc, given several methanol washes, and finally air dried.

Method 8 This experiment is the same as method 7 except that afterreduction of the quinone 3 grams of catechol are added with 5 grams oftrioxane and the procedure is carried as described.

Method 9 10 grams of naphthazarin (5.8 dihydroxy 1,4 naphthoquinone)were dissolved in 200 ml. glacial acetic acid and 20 ml. of 96% sulfuricacid. 15 grams of zinc dust were added and the mixture boiled until theoriginal red solution became a light grayish green. The naphthazarinpersion medium.

anol, and dried.

Method 10 20 grams of ca-techol and f5 :grams 'oftrioxane were suspendedin 200 ml. of ligroin (boiling range 90 120) The mixture was heated to70" with stirring (about 300 rpm). To this two phase liquid system wasadded 5 ml. of 96% sulfuric acid. The temperature was then raised to theboiling point and the mixture "stirred 'for 8 hours. The resultingpolymer was filtered, boiled up with several portions of methanol toextract 'solubles, and

dried. Most of this material consisted of spheroidal particles. Particlesize can be controlled to a large extent by temperature variation andstirring rate. A small amount of material deposited as a film on theflask 'sur- 2 face. 0

Method 11 The details of this experiment were the same as Method 10except that kerosene or hexyl chloride was the disthe mediumwasmaintained at 110' .C. :10 instead of at the boiling point after all,the ingredients had been added.

In all of these methods the yield of polymer was quantitative, based onthe amount of .polyhydric phenol as .30

the limiting reactant; I

All the resins herein described reduce ferric "ion, ferricyanide ion,and iodine. The following "is an outline of the method employed todemonstrate the reversible redox properties of these resins. (materialprepared in Example 10, Table I) was packed into a Jones reductor (2.5cm. diameter) between plugs of glass wool. The height of the resincolumn was 15 cm. grams of ferric chloride hexahydrate were dis- Inthese experiments the temperature of 5 25 grams of dry resin the columnwith the aid of suction. eluate colprices and gave negative tests forferric ion with sium thiocyanate and beta-resorcylic acid solutions.This colourless solution on treatment with sodium ferricyanide gavelatypical prussian blue precipitate showing the presence of ferrous ion inthe eluate. result was continued by the oxidation of a portion of theeluate with hydrogen peroxide, followed by the addition ofbetaresorcylic acid to give a typical red-purple color.

The column can be reactivated by the use of solutions of reductants suchas .chromous chloride or sodium hy- .drosulfite. An electrolytic methodwas also devised such that the resin column was made the cathode of anelectrolytic cell. After reduction the column is washed free of foreignmatter with dilute mineral acid ,afollowed by distilled water.

The same resin column after reactivationwasused :to demonstrate thereduction of sodium ferricyanide and iodine in aqueous solution. 2 gramsof sodium ferricyanide in 100 ml. of water was passed through in 15minutes. The eluate was light yellow and gave :a positive test forferrocyanide ion and a negative test for ferricyanide ion. The columnwas washed down with tap Water, dilute hydrochloric acid, and finallydistilled water until the eluate was free of foreign ions. 100 m1. of asaturated aqueous iodine solution was passed through.

The eluate showedyno trace of iodine, but gave a copious precipitate ofsilver iodide on addition of silver nitrate.

viously described. 'For example, 1,4,5,8 tetrahydroxynaphthalene reducesferric ion, ferricyanide ion, and iodine. In these reactions eachpolyphenol unit presumbably goes to the oxidation state analogous tonaphthazarin. However, I have shown that stronger oxidants such aschromic acid and ceric sulfate oxidize the polymer to the diquinonestate. In that state the polymer in turn oxidizes ferrous, ferrocyanide,and iodide ions. The

solved in 300 ml. water and this solution was run through 40 sameobservations have been made with 1,2,4,5 tetra- TABLE I.SUMMARY OFEXPERIMENTS Polyhydroxyphenol Aldehyde or derivative thereof Solvent orDispersion Conditions and Remarks Method medium 37% sq. formaldehyde 40%sq. chloroacetaldehyde.

gelled then boiled dn 30% no. glyoxal 30% no. glycollicaldehyde--.

40% sq. chloroacetaldehydc fnrfural 2,2 dihydroxy hiphenyl-.. H2804..-"6 I 29 1,4,8); tetrahydroxynaph- H 9 t a 30.. ligroln (120 O.) 13280 102; 31-. d kern erw H;S0 ll 32 .do hexyl chloride H 50..- 11 1% riuriural. ligroin (90l20 O.) H280 10 R4 pyrng-illnl trinxam: dn H2SO4 1O35 r n do H SO 10 36 .do furfural. HlSO b led l0 isopropanol ethyleneglycol diethyl ether-.-

methyl isobutyl ketone ethylene glycol dimethyl etheracetic acid l,2.4,5tetrahydroxy benzene.

1,2,4.5 tetrahydroxy benzene+catechol.

pentanydroxy benzene+ catechol.

gallic acid catecholi-sulfonic acid...

1,2 dihydroxy naphthalene-i-sullonic acid.

1,%,5 trihydroxy naphthaenc.

'hydroxy' "benzene polymers. Thus, many of the common redox couples canbe either oxidized or reduced depending on the oxidation state of theresin.

'- I have also found these chelating resins to be useful in bindingmetal ions. These experiments were carried out in the same fashion asthe redox ones. For example, a 0.1 molar solution of cobaltous chloridewas passed through the resin column. The excess was washed out withdistilled water until the eluate was free of cobalt ion. 1 molarhydrochloric acid was then passed through, and cobalt ion wasdemonstrated in the eluate. Similar results were obtained with nickelchloride, ferrous sulfate, uranyl acetate, lead nitrate, mercuricchloride, and cadmium chloride. 3 Having so described my invention, I donot limit myself to the specifically mentioned times, temperatures,quantities of chemicals, or steps of procedure, as these are givensimply to clearly describe my invention as set forth in my specificationand claims, and they may be varied without going beyond the scope of myinvention.

I claim: a a

1. An insoluble infusible, cross linked, redox resin which is the acidcondensation product with an aldehyde material selected from the groupconsisting of an aliphatic aldehyde, furfural, and a compound capable ofyielding an aliphtic aldehyde under the reaction conditions, of apolyhydroxylated phenol of not more than twelve aromatic ring carbonatoms, all of said ring carbon atoms being bound to each other bycarbon-carbon bonds, having four to five hydroxyl groups attached tosaid aromatic carbon atoms, having two pairs of phenolic hydroxyl groupscapable of forming metallic chelates and having at least one aldehydereactive position on the aromatic ring, there being in addition to saidpolyhydroxylated phenol also the phenol, catechol, as the soleadditional phenol whenever'the numberof aldehyde reactive positions onthe aromatic ring of the polyhydroxylated phenol is less than three,said polyhydroxylated phenol being oxidizable to a quinone, the ratio ofthe number of moles of said aldehyde material to the number of moles oftotal phenol being in the range of 1.1-2.5 to 1.

2. A resin according to claim 1 wherein th epolyhydroxylated phenol is1,4,5,8 tetrahydroxynaphthalene and the aldehyde materialisformaldehyde.

3. A resin according to claim 1 wherein the phenol content is 1,2,4,5tetrahydroxybenzene and catechol and the aldehyde is formaldehyde.

References Cited in the file of this patent UNIT ED STATES PATENTS2,275,923 Ross Mar. 10, 1942 2,304,431 Walker Dec. 8, 1942 2,477,641Nagel Aug. 2, 1949 2,478,943 Rhodes Aug. 16, 1949 2,700,029 Cassidy Jan.18, 1955 2,703,792 Kropa Mar. 8, 1955 OTHER REFERENCES Adams et al.: J.Soc. Chem. Ind., Jan. 11, 1935, pages IT to GT.

Wang et al.: J. Chem. Eng. China, vol. 16, pages -28, 1949, abstractedin C. A., 368, Jan. 10, 1950.

.Manecke, Z. F.:- Electrochemie, vol. 57, No. 3, April 1953, pages189-194.

1. AN INSOLUBLE, INFUSIBLE, CORSS LINKED, REDOX RESIN WHICH IS THE ACIDCONDENSATION PRODUCT WITH AN ALDEHYDE MARERIAL SELECTED FROM THE GROUPCONSISTING OF AN ALIPHATIC ALDEHYDE, FURFURAL, AND A COMPOUND CAPABLE OFYIELDING AN ALIPHTIC ALDEHYDE UNDER THE REACTION CONDITIONS, OF APOLHYDROXYLATED PHENOL OF NOT MORE THAN TWELVE AROMATIC RING CARBONATOMS, ALL OF SAID RING CARBOB ATOMS BEING BOUND TO EACH OTHER BYCARBON-CARBON BONDS, HAVING FOUR TO FIVE HYDROXYL GROUPS ATTACHED TOSAID AROMATIC CARBON ATOMS, HAVING TWO PAIRS OF PHENOLIC HYDROXYL GROUPSCAPABLE OF FORMING METALLIC CHELATES AND HAVING AT LEAST ONE ALDEHYDEREACTIVE POSITION ON THE AROMATIC RING, THERE BEING IN ADDITION TO SAIDPOLYHYDROXYLATED PHENOL ALSO THE PHENOL, CATECHOL, AS THE SOLEADDITIONAL WHENEVER THE NUMBER OF ALDEHYDE REACTIVE POSITIONS ON THEAROMATIC RING OF THE POLYHYDROXYLATED PHENOL IS LESS THAN THREE, SAIDPOLYHYDROXLATED PHENOL BEING OXIDIZABLE TO A QUINONE, THE RATIO OF THENUMBER OF MOLES OF SAID ALDEHYDE MATERIAL TO THE NUMBER OF MOLES OFTOTAL PHENOL IN THE RANGE OF 1.1-2.5 TO 1.